Field of the Invention
The invention relates to a monolithic multiple solar cell made from elements of the 3rd and 5th main groups of the periodic table of elements with an integrated semiconductor mirror.
Description of the Background Art
A corresponding double solar cell (also called tandem cell) is known from the publication “Prog. Photovol: Res. Appl. 2001; 9:165-178, F. Dimroth et al. Metamorphic Ga.sub.yIn.sub.1-yP/Ga.sub.1-xIn.sub.xAs Tandem Solar Cells for Space and for Terrestrial Concentrator Applications at C>1000 Suns.” As the integrated semiconductor mirror a Bragg mirror is used. The Bragg mirror is thus epitaxially applied on a GaAs substrate, on which in turn the double solar cell GaInP/GaInAs, which has an n to p polarity, is epitaxially applied.
From Physica E. 2002, Vol. 14, p. 84-90, M. Yamaguchi: “Multi-junction Solar Cells and Novel Structures for Solar Cell Applications”, simple and multiple solar cells are known, wherein a Bragg reflector may be disposed on the rear side of the simple solar cells.
From the Journal of Electronic Materials, Vol. 21, No. 3, 1992, S. M. Vernon et al. “Growth and Characterization of Al.sub.xGa.sub.1-xAs Bragg reflectors by LP-MOCVD”, a GaAs solar cell with a Bragg reflector on a silicon substrate is known.
From the publication “Solar Energy Materials & Solar Cells 68 (2001), p. 105-122, M. Z. Shvarts et al. “Radiation Resistant AlGaAs/GaAs Concentrator Solar Cells with Internal Bragg Reflector”, a GaAs simple solar cell is known, under which a Bragg mirror is disposed. The solar cell used is a cell with a p to n polarity.
From WO-A-2004/017425, a multiple solar cell is known, in which back reflectors, which carry out the function of the electric mirrors in relation to the minority carriers, run between the individual solar cells.
Lattice-matched triple solar cells of Ga.sub.0.5In.sub.0.5P/Ga.sub.0.99In.sub.0.01As/Ge are market leaders among the space solar cells. The best cells reach 30-31% efficiency under the space solar spectrum AMO. In production, so far a maximum average efficiency of at least 28.3% was achieved. A decisive factor is the radiation hardness of the cells. According to a typical irradiation with 1.times.10.sup.15 cm.sup.-2 1 MeV electrons, the efficiency of these cells is degraded to 24.3%. This corresponds to a residual factor of 86%.
Quintuple to sextuple solar cells are described in “Solar Cell Manufacturers Come Back Down to Earth” by M. Hatcher, Compoundseminconductor.net magazine, November 2003.